Heat transfer unit: The design, construction, and operation are discussed of liquid metal loops to deal with a high temperature heat transfer system of 1000 kw energy transfer capacity within the temperature range of 1000 to 1350 F. An Allis-Chalmers 1A pump was installed in a test loop, and performance tests were run at the 1000-kw NaK conditions. The pump operated successfully at 130 gal/min while delivering 28 psi total dynamic head at temperatures to 1150 F. The pump efficiency was 11.4% at these conditions. Engineering: Natural circulation with NaK is being studied on the shell side of a vertical unbaffled 19-tube stainless steel heat exchanger. The single-tube steam generator was built to test the performance of the suggested double wall tubes to be used in the 1000-kw heat transfer unit steam generator. Three tubes have been tested. Chemistry: The behavior of Fe in Na is being investigated as a function of O content, Na temperatures, and cold trap temperature. Corrosion tests were made on various metals which had been exposed to NaK at 1500 F for 500 hr. An Inconel specimen, after being tested, showed at 3% weight gain and was found to be magnetic. The stainless steel specimen holder also became corroded and magnetic. The O content varied from 0.028 to 0.107%. Materials suitable for electrical insulation have been exposed to NaK at 250 and 300 F.